I think it's not unusual to have base-x number literals (even Python got `0b01101` literals at some point), but not many languages support pattern matching on bitstrings. In Erlang, it looks like this:

    1> A = 2#0010010010101001.
    9385
    2> << _:2, B:4, _/bitstring >> = << A:16 >>, B.
    9
    3> io:format("~.2B~n", [B]).
    1001

I put your number into 16-bit bitstring[1], then ignored first 2 bits, extracted the next 4 bits, and ignored the rest.

CL doesn't have pattern matching in the standard, IIRC, but there are libraries implementing it, so I wouldn't be surprised if one of them also offered bitstring matching, but that's beside the point: I'm comparing Erlang and C++ here, not Erlang and CL.

[1] It could be 14 or 15 bits, but I wanted to have a bit of a leading padding to ignore in the pattern.

EDIT: I missed the fact that the #*01... literal in CL is not a number, my bad. The equivalent literal would be << 2#01...:N >> in Erlang, but you need to give the N (number of bits) yourself, so it's a bit less convenient.